1. Field of the Invention
The present invention relates to a wear and impact resistant polycrystalline diamond composite for use in rock drilling, machining of wear resistant substances, and other operations which require the high abrasion resistance or wear resistance of a diamond surface. Specifically, this invention relates to such bodies that comprise a polycrystalline diamond layer attached to a cemented metal carbide substrate by way of processing at ultrahigh pressures and temperatures or by chemical vapor deposition.
2. Description of the Art
Composite polycrystalline diamond compacts, PCD, have been used for industrial applications including rock drilling and metal machining for many years. One of the factors limiting the success of PCD is the strength of the bond between the polycrystalline diamond layer and the sintered metal carbide substrate. For example, analyses of the failure mode for drill bits used, for deep hole rock drilling show that in approximately 33 percent of the cases, bit failure or wear is caused by delamination of the diamond from the metal carbide substrate.
U.S. Pat. No. 3,745,623 (reissue U.S. Pat. No. 32,380) teaches the attachment of diamond to tungsten carbide support material. This, however, results in a cutting tool with a relatively low impact resistance. FIG. 1, which is a perspective drawing of this prior art composite, shows that there is a very abrupt transition between the metal carbide support and the polycrystalline diamond layer. Due to the differences in the thermal expansion of diamond in the PCD layer and the binder metal used to cement the metal carbide substrate, there exists, after fabrication at ultrahigh pressure and temperature, a stress in excess of 200,000 psi between these two layers. The force exerted by this stress must be overcome by the extremely thin layer of cobalt which is the binding medium that holds the PCD layer to the metal carbide substrate. Because of the very high stress between the two layers, which is distributed over a flat narrow transition zone, it is relatively easy for the compact to delaminate in this area upon impact. Additionally, it has been known that delaminations can also occur on heating or other disturbances aside from impact. In fact, parts have delaminated without any known provocation, most probably as a result of a defect within the interface or body of the PCD which initiates a crack and results in catastrophic failure.
U.S. Pat. No. 5,011,515 discusses numerous attempts by previous inventors, as shown in FIGS. 2 and 3 herein, to solve the problem of delamination of the polycrystalline diamond layer from the metal carbide substrate. U.S. Pat. No. 4,604,106 teaches the use of transitional layers in order to lessen the concentration of stress at the interface between the two layers, but the method described reduces overall bonding strength by introducing impurities and preventing the cobalt or other binder metal of the substrate from cleanly sweeping through the diamond layer, which is necessary for good sintering action. U.S. Pat. No. 4,784,023, as shown in FIG. 3 herein, and U.S. Pat. No. 4,592,433 teach parallel grooving of substrates to form ridges for increased bonding surface area. Similarly, U.S. Pat. No. 5,351,772 teaches the use of upwardly-projecting lands which extend radially.
These designs produce stress in some portions of the cutter which is actually higher than that exhibited in the planar interface of a PCD manufactured according to the teachings of U.S. Pat. No 3,745,623 (reissue U.S. Pat. No. 32,380). Finite element analysis (FEA) shows that three-dimensional surfaces do not eliminate this stress; however, they do redistribute the stress into localized areas, some of which are higher in stress and some of which are lower in stress. In order to take advantage of this redistribution, the geometry of the surface must be engineered so that if a crack is initiated it has difficulty in propagating across the interface or through the body of the cutter. Prior art shows a number of three-dimensional designs which all have essentially the same problem; namely, localized high concentration of stress which serves to initiate a fracture and a straight line or path for the initial fracture to follow.
Likewise, U.S. Pat. No. 5,379,854 shows the formation of ridges on non-planar substrates; i.e., substrates which utilize a hemispherical cap as the interface between the polycrystalline diamond and metallic carbide support. In this instance as in the others, regions of alternating stress are present, and the higher stress areas result in formation of a crack or other type of flaw at the interface between the diamond and carbide support which then is propagated easily along the lines of the ridge or along the smoothly curving surface of the hemispherical interface.
U.S. Pat. No. 5,355,969 teaches the use of three dimensional protuberances spaced apart in a radial direction from the axis of a planar support surface. This offers some advantage over that of a clearly defined ridge since once initiated a crack does not have a single planar side wall or ridge along which to propagate. However, as a result of the specific radial distribution of these protuberances, a crack can propagate easily either radially along a spoke or in a circumferential direction between the protuberances.
U.S. Pat. No. 5,011,515 teaches the use of surface irregularities spread in near uniformity across the substrate mounting surface in a patterned or in a random manner to control the percentage of diamond in the zone that exists between the metal carbide support and the polycrystalline diamond layer. This serves to spread uniformly the alternating bands of stress and, in the case of random distribution of protuberances, does not provide an easy path for a fracture to propagate. Conversely, in the case of a patterned distribution of surface irregularities, a crack can propagate easily in any number of directions, along a straight line between the protuberances.
It would be desirable to have a three dimensional substrate mounting surface with a topography which would distribute uniformly the unavoidable stress in a predetermined pattern without a simple or obvious pathway for a crack, once initiated, to propagate anywhere within the interface between the polycrystalline diamond and metal carbide substrate.